F. R. Frajprie — Chromates of Caesium. 311 



The apparatus thus prepared was screwed up tight, con- 

 nected with the oxygen generator, and heat applied to the lat- 

 ter until a sufficient pressure was reached, or until all the oxy- 

 gen had come off. The generator was detached, and the bomb 

 kept at the desired temperature in the thermostat for a period 

 of from one to seven days. When opened, the crystals, if any 

 were found, were removed from the liquid as hastily as pos- 

 sible, dried between filter papers, and examined. In the 

 whole series of forty experiments not a single measurable crys- 

 tal was obtained, the crystalline powder always consisting of 

 irregular fragments mingled with very minute crystals. A 

 microscopic examination often showed small perfect crystals. 



Shortly before the end of the work in Cambridge, one crop 

 of crystals was obtained at a pressure of twenty-eight atmos- 

 pheres by heating the bomb in the thermostat at 70° for eight 

 hours, and allowing it to cool slowly over night in the large tank 

 of water. An excess of salt had been added to the solution, and a 

 fair crop of crystals was obtained. While these was consider- 

 ably etched, they gave readable signals, and from measure- 

 ments of a number of crystals, it was found that the angles 

 were the same, within the limits of error of reading, as on crys- 

 tals grown under ordinary conditions. 



The crystals of this crop differed in habit from those pre- 

 viously obtained, in that the predominant terminating plane was 

 a rhombohedron, well developed on both ends of the crystals, 

 and with its edges truncated by a pair of narrow faces of the 

 pyramid ordinarily present. The faces of this rhombohedron 

 were often slightly concave. For this reason, and because 

 only ten faces could be measured, the axial ratio was calculated 

 from the pyramid. The measurements follow : 



Cs 2 Cr0 4 a (Rhorabolieclral-hemihedral). 

 a : c = 1 : 1-2314. 









Calcu- 





Read- 











lated. 



Measured. 



ings. 



Limits. 



a r 



1010 



I'O'Il - ... 



.. 25° 1' 



25° 0' 



10 



25° 19'-24° 21' 



b p 



1120 



1123 





*50 37 



34 



50 42-50 36 



r r 



lOll 



0111 



103 16 









Cleavage : basal, incomplete. 



Forms : a (1010), b (1120), r (1011), p (1123). 



The habit of the crystals is shown in figs. 1 and 2. Fig. 1 

 shows the crystals grown under ordinary pressure ; they were 

 apparently holohedral, invariably fully developed, with the six 

 pyramid faces on each end all nearly equal in size, and with 

 no trace of any rhombohedral face. Fig. 2 shows the rhom- 

 bohedral crystals grown under pressure. 



